Which of the following best describes non-renewable resources?

Non-renewable resources are defined as materials that exist in finite quantities and cannot be replenished on a human timescale once they are exhausted. This category includes fossil fuels like coal, oil, and natural gas, as well as certain minerals and metals. Once these materials are extracted and consumed, they take millions of years to form naturally, which means they cannot be quickly replaced. This characteristic differentiates non-renewable resources from renewable resources, which can be replenished over relatively short periods of time, such as solar energy, wind energy, and biomass.

The other options do not accurately describe non-renewable resources. For instance, the statement about resources being consumable repeatedly applies to renewable resources that can be regenerated, which is not the case for non-renewables. Likewise, the mention of sustainable practices pertains to the management of resources but does not reflect the nature of non-renewable resources. Lastly, while non-renewable resources may sometimes be harvested easily, this does not define them and overlooks the fact that their availability is limited and unsustainable in the long term. Thus, the correct characterization of non-renewable resources is that they cannot be quickly replaced once used, as highlighted in the chosen answer.